A CR-39 has good advantages such as cumulative type dosimeter, small fading effect and gamma-ray insensitive. Therefore, we developed the wide energy-range environmental neutron dosimeter using eight CR-39s for area monitoring in this study. This dosimeter is made of octagonal columnar polyethylene block which height is 60 mm and bottom side is 25 mm. The dosimeter contains two types of CR-39s for fast neutron detection and slow neutron detection. Four CR-39s for fast neutron detection are used for detection of recoil protons produced by H (n, p) reactions. Four CR-39s for slow neutron detection are used with boron nitride converter to detect alpha-rays produced by 10B (n, α) 7Li reactions. Ambient dose equivalent is obtained by adding the number of etch-pits observed in four CR-39s for fast neutron detection to the number of etch-pits observed in four CR-39s for slow neutron detection with appropriate constants respectively. Dosimeters were irradiated with some energetic neutrons and evaluated results of ambient dose equivalent were compared with results from neutron transport calculations. Energy response of dosimeter shows good agreement with neutron fluence to ambient dose equivalent conversion coefficients. Directional dependence of dosimeter is at the same level as the rem-counter.
In IAEA SRS No. 44, clearance levels for radionuclides of natural origin (e. g. U-235 and U-238) are judged to be 1 Bq/g from consideration of the upper end of the worldwide distribution of activity concentration in soil. However, a result of estimating the radiological effect of the clearance level is not shown. In this paper, in order to confirm the radiological effect of the clearance level (1 Bq/g) based on the activity concentration in ubiquitous unmodified soil, we estimate the clearance levels for major radionuclides of U-234, U-235 and U-238 in the solid materials contaminated with uranium on the basis of dose calculation approach for radionuclides of artificial origin in IAEA SRS No. 44, which are generated from the processes of nuclear fuel cycle facilities such as conversion, enrichment and fuel manufacturing. The activity concentrations of U-234, U-235 and U-238 are calculated to be 1.2 Bq/g, 0.53 Bq/g and 1.1 Bq/g respectively for applying effective dose criteria and a skin equivalent dose limit. It is confirmed that the activity concentrations estimated using the dose calculation approach are consistent with the clearance levels of IAEA derived on the basis of the worldwide distribution of activity concentration in soil.
The purpose of the present paper is to review ICRP Publication 110 entitled “Adult reference computational phantoms”.1) In its recent recommendations, the ICRP adopted these computational phantoms for the forthcoming update of organ dose coefficients for internal and external radiation sources. The phantoms are based on medical image data of real persons and are consistent with the information given in ICRP Publication 89 on the reference anatomical and physiological parameters for both male and female subjects. The reference voxel models were constructed after modifying the voxel models of two individuals whose body height and mass closely resembled the reference data. The organ masses of both models were adjusted to the ICRP data on the adult Reference Male and Reference Female, without significantly altering their realistic anatomy. The ICRP publication describes the methods used for this process and the characteristics of the resulting voxel phantoms. Furthermore, the applications of these phantoms intended by ICRP and ICRU are indicated, and the phantoms' limitations are highlighted. The phantoms' technical descriptions as well as graphical illustrations of conversion coefficients for some external and internal exposures are presented in a series of Annexes to ICRP Publication 110. In addition to ICRP Publication 110, the present paper shortly characterises intermediate versions of the reference computational phantoms that are referred in the literature.
The latest knowledge encompass findings presented both in individual scientific publications and in internationally accepted reports. This review summarizes the latest knowledge on radiobiological effects on the latter level, using studies of atomic bomb survivors and victims of Chernobyl nuclear power plant accident. First of all, it is important to note that while examining individual patient, it is impossible to distinguish a radiation-induced cancer patient and non-radiation-induced cancer patient even when using state-of-the-art techniques. Therefore, investigation of radiation effects on humans, especially late health effects has been based on the epidemiological and statistical methods. Based on studies on atomic bomb survivors, it is well accepted that there is a linear increase in the risk of cancer with the increase of radiation dose. However, the existence of a threshold is a controversial issue, and health effects with regards to non-cancer diseases are not yet accepted by international authorities. Childhood thyroid cancer has increased after the Chernobyl accident and more than several thousands children are affected by it. However, there is no proof that any disease, with the exception of thyroid cancer and acute radiation effects, has increased after the Chernobyl accident. Finally, it should be mentioned that providing scientific explanation of the results to general public is an honorable duty of concerned scientists.